In many enclosures for electronic devices such as computers, storage devices, game consoles or audio-visual equipment, the heat generated by the electronic components must be vented to the exterior of the enclosure. Typically, one or more direct current (DC) fans are used for that purpose. When the temperature within the enclosure reaches a given threshold, the fan is commanded to turn on at full speed. This can result in audible noise that may become bothersome to the user.
Some implementations sense the temperature within the enclosure and modulate the speed of the fan according to the sensed temperature. This can result in a quieter fan operation profile. However, such fan speed modulation is accomplished using a costly fan speed control integrated circuit (IC) that can be overly sensitive to small changes in the duty cycle of the pulse width modulation (PWM) input control signal. What are needed, therefore, are DC motor controllers that are less costly and that nevertheless provide an increased dynamic range and a fine control of the speed of the fan.